C. elegans locomotion is modulated by its present environment and past experience. When well-fed animals encounter food, their rate of locomotion decreases. When food-deprived animals encounter food, they slow their rate of locomotion substantially more, termed the enhanced slowing response. Although serotonergic neurotransmission is known to play a central role in the enhanced slowing response, currently there is no information on how the two inputs (the presence of food and the food-deprived state) are signaled and integrated to modulate locomotion. The molecular components and mechanisms that are required for the modulation of locomotion will be identified in experiments outlined in this proposal. Specifically, genetic screens will be employed to identify novel mutations which affect the enhanced slowing response. The mutants will be behaviorally and genetically characterized followed by the cloning of several of the more interesting mutants. Finally, the enhanced slowing response neural circuits will be defined using a combination of GFP reporters and laser ablation. The completion of these aims will provide insights into the modulation of behavior that should further the field of neurobiology. [unreadable] [unreadable]